Cardiac hypertrophy and heart failure are major causes of morbidity and mortality worldwide. These syndromes result from a variety of hemodynamic and humoral pathophysiologic stimuli, including hypertension, ischemia, and myocardial infarction. At the cellular level, protein kinase signaling cascades transduce extracellular signals into characteristic molecular and structural changes in the cardiac myocyte, which frequently includes alterations in normal energy production via dysregulation of mitochondrial fatty acid [unreadable]-oxidation (FAO). The principal transcriptional regulator of FAO enzyme genes in heart, the peroxisome proliferator-activated receptor a (PPARa), has been shown to be deactivated by an extracellular signal-regulated kinase (ERK)-dependent process during cardiac hypertrophy, contributing to decreased FAO enzyme expression and loss of fatty acid oxidative capacity. Conversely, p38 mitogen activated protein kinase (MAPK) activation increases PPARa transcriptional activity via a direct phosphorylation event and enhances FAO in cardiac myocytes. This proposal is designed to understand the mechanisms whereby MAPK pathways differentially regulate the activity of PPARa in response to cellular stressors in the heart. This will be accomplished by i) identification of specific p38 MAPK phosphorylation sites on PPARa utilizing EMSA, ligand-binding assays, and protein-protein interaction assays; ii) determination of the mechanism by which ERK MAPK deactivates PPARa via in vivo phosphorylation studies, EMSA, ligand-binding assays, protein-protein interaction assays, co-immunoprecipitation assays in myocytes, and cotransfection assays with candidate repressors of PPARa activity; iii) definition of pathway specific regulation of PPARa target gene expression in vitro and in vivo and elucidation of the consequences of non-selective MAPK activation on PPARa activity; iv) identification of novel cardiac-expressed PPARa-interacting proteins via yeast two-hybrid and proteomics approaches. Modulation of the PPARa gene regulatory pathway by MAPK family members offers the potential to understand fundamental mechanisms whereby multiple signaling pathways integrate on a single transcription factor. We speculate that regulation of PPARa signaling is an integral component of the cellular stress response with implications for downstream modulation of cellular energy metabolism. [unreadable] [unreadable]